Information stored on an optical disc commonly appears as a spiral track known as an information track. The spiral information track of an optical disc is similar in appearance to the spiral grove of a vinyl record. There are varying types of optical discs that can be used for recording information. One type is a blank optical disc with no pre-manufactured tracks. Another type is an optical disc containing pre-manufactured information tracks for recording information. The method for recording information on each of these types of optical discs depends on the type of disc being used.
One method for recording information on a blank optical disc that does not have pre-manufactured tracks is referred to as mastering. Optical disc mastering involves recording information on a master optical disc that is subsequently used to directly or indirectly create replicating stampers for mass producing optical discs. Recording information on a master optical disc starts with a blank master optical disc having no pre-manufactured tracks. A mastering machine records information on a blank master disc by moving an optical head radially across the disc as the disc rotates. A blank master disc, however, has no information on the recording surface to aid a mastering machine in moving an optical head radially across the optical disc during the recording process. Therefore, mastering machines typically use a precision machined lead screw or a precision calibrated interferometer to move the optical head radially across the disc during the recording process, thus causing spiral tracks to be formed on the disc.
As alluded to above, optical disc mastering is primarily used by optical disc manufacturers that mass produce optical discs. Mastering machines tend to be very expensive and highly involved machines that are not well suited for consumer end-use. It may be worth noting that the actual master disc itself uses highly specialized and expensive optical disc technology that also makes it not well suited for consumer end-use.
In recent years, advances in optical disc technology has made it possible to economically manufacture optical disc recorders and recordable optical media as commercially viable consumer end-products. Examples of this technology include magneto optical (MO) discs and drives, mini-discs and mini-disc recorders, write-once-read-many (WORM) discs and drives, and compact disc recordable (CD-R) discs and drives. All of these technologies share the common feature of recording information on an optical disc that has pre-manufactured tracks for recording information. One reason for using discs with pre-manufactured tracks for recording information is to take advantage of established optical disc tracking technology used by compact disc players and video laser disc players. This tracking technology uses a tracking servo that takes advantage of existing tracks on an optical disc. The tracking servo keeps the optical head of a machine in line with either an information track or a track for recording information as the disc rotates by sensing the location of the track. The location of the track is determined by measuring the intensity of the beam reflected by the disc with a photodetector array. The intensity of a beam reflected by an optical disc is the least when the beam is reflected by either the information track portion of the disc or the track portion of the disc for recording information.
Thus, another method of recording information on an optical disc is by using optical discs with tracks for recording information manufactured directly into the recording surface of the disc.